Preliminary design and performance assessment of compressed supercritical carbon dioxide energy storage system

Energy storage system plays a key role in the network grid with the increasing penetration of intermittent renewable energy. Compared with the compressed air energy storage system, the energy storage with compressed supercritical carbon dioxide has the advantages of compactness and high energy storage density. In this paper, we propose two isobaric compressed supercritical carbon dioxide energy storage systems: a simple cycle system and a split cycle system. Underwater energy bags are firstly adopted to store the compressed carbon dioxide and maintain a constant gas pressure during charging and discharging processes. Energy and exergy performance of the systems are analyzed, and the exergy economics is presented for the proposed compressed carbon dioxide energy storage systems. The effect of key parameters on the system performance is performed. The results show that the simple cycle has a lower round trip efficiency (38.74%), a lower exergy efficiency (55.85%) and a slightly better economic performance. The split cycle performs with a higher round trip efficiency (43.94%) and a higher exergy efficiency (62.81%). Total investment cost per unit output work of the split cycle (0.0726 $/kWh) is higher under the condition of free heat source. It can be concluded that the split cycle can enhance the thermodynamic performance of the energy storage system by improving the design of the recuperator.